A silicon carbide MPS diode with high surge current

Abstract

This invention discloses a silicon carbide MPS diode with high surge current, comprising a cathode ohmic contact electrode, a silicon carbide N+ substrate, and a silicon carbide N- epitaxial layer stacked sequentially. Multiple P+ injection regions are spaced apart on the silicon carbide N- epitaxial layer, and ohmic contact electrodes are disposed on the P+ injection regions. The gaps between the ohmic contact electrodes are filled with Schottky contact electrodes. Bipolar transport layers are disposed on both sides of the silicon carbide N- epitaxial layer. Due to the presence of the variable-doped bipolar transport layers, the PN junction forward voltage of the MPS diode is reduced, allowing the diode to enter the bipolar operating state earlier at a lower current. This results in a conductivity modulation effect, reducing the diode's on-resistance and lowering the chip temperature under high current, thereby improving the diode's surge current resistance and reverse breakdown voltage.

Description

Technical Field

[0001] This invention relates to the field of diode technology. Background Technology

[0002] Silicon carbide (SiC), a wide-bandgap semiconductor material, is an ideal material for fabricating high-voltage power electronic devices. Compared to Si, SiC has a higher breakdown electric field strength (4 × 10⁻⁶). 6 V / cm), high carrier saturation drift velocity (2×10⁻⁶ V / cm), and high carrier saturation drift velocity (2×10⁻⁶ V / cm). 7 With advantages such as high thermal conductivity (cm / s), high thermal conductivity, and good thermal stability, silicon carbide (SiC) junction barrier Schottky diodes (JBS) are particularly suitable for high-power, high-voltage, and high-temperature applications. As the earliest commercially available SiC power device, it still holds the largest market share. Through the potential barrier formed by the contact between the SiC semiconductor and the metal, it achieves a rectification effect of conducting in one direction and blocking in the other. JBS diodes offer advantages in power systems, including low on-resistance and high breakdown voltage, low conduction loss, fast switching speed, and near-ideal reverse recovery characteristics, making them highly advantageous in high-frequency, high-power power electronics applications.

[0003] Diodes used in switching power supplies must be able to withstand surge currents, which are the peak currents flowing into the power supply device at the moment of power-on. Because the input filter capacitor charges rapidly, this peak current is much larger than the steady-state input current. The recurring surge current of a typical SiC JBS diode can be 4-5 times its steady-state operating current. To improve the reliability of SiC JBS devices in switching power supplies, the diode's surge current resistance needs to be enhanced. Therefore, an ohmic contact is created above the PN junction of the JBS diode, forming an MPS (Merge-PiN-Schottky) diode structure. Using an MPS structure can increase the surge current to 10-13 times the steady-state operating current.

[0004] The surge current of a silicon carbide (SiC) JBS diode depends on the Schottky junction current capability of the chip. After fabricating the gold-plated contact above the PN junction into an ohmic contact to form an MPS diode structure, the surge current capability depends on the current magnitude of the diode in bipolar operation. For MPS diodes, the PN junction conducts under surge current impact, causing the diode to operate in a bipolar state, resulting in a conductivity modulation effect. This reduces the diode's on-resistance and operating temperature, improving the device's surge current resistance. Therefore, the PN junction of an MPS diode must conduct under surge current impact to achieve the desired surge current resistance. However, in the normal operating state of a conventional MPS diode, the Schottky junction current dominates. To ensure that the operating current meets requirements under normal operation, the PN junction area is usually a small proportion of the total chip area. This small PN junction area results in a large PN junction forward voltage, meaning the PN junction may not conduct under surge current impact, causing premature diode failure. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to realize a diode that reduces the PN junction forward voltage drop of MPS diode under the same PN junction area ratio, thereby improving the surge current resistance capability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a silicon carbide MPS diode with high surge current, which is composed of a cathode ohmic contact electrode, a silicon carbide N+ substrate, and a silicon carbide N- epitaxial layer stacked sequentially. A plurality of P+ injection regions are spaced apart on the silicon carbide N- epitaxial layer, and ohmic contact electrodes are provided on the P+ injection regions. The gaps between the ohmic contact electrodes are filled by Schottky contact electrodes, and bipolar transport layers are provided on both sides of the silicon carbide N- epitaxial layer.

[0007] The bipolar transport layer between the P+ implantation region and the silicon carbide N- epitaxial layer is the first bipolar transport layer, and the bipolar transport layer between the bipolar transport layer and the silicon carbide N+ substrate is the second bipolar transport layer. The first bipolar transport layer includes the P+ implantation region, and the thickness of the bipolar transport layer is greater than the depth of the P+ implantation region.

[0008] The first bipolar transport layer and the second bipolar transport layer have the same thickness.

[0009] The doping concentration of the bipolar transport layers is lower than that of the silicon carbide N-epitaxial layers.

[0010] The first bipolar transport layer and the second bipolar transport layer have the same doping concentration.

[0011] The impurity doping distribution of the bipolar transport layer is linear, with the doping concentration decreasing from top to bottom.

[0012] The first bipolar transport layer and the second bipolar transport layer have the same impurity doping distribution.

[0013] The highest doping concentration of the bipolar transport layer is the same as that of the silicon carbide N-epitaxial layer.

[0014] The MPS diode of this invention, due to the presence of a variable-doped bipolar transport layer, reduces the PN junction forward voltage, allowing the diode to enter the bipolar operating state earlier at a lower current. This results in a conductivity modulation effect, reducing the diode's on-resistance and lowering the chip temperature under high current, thereby improving the diode's surge current resistance. Simultaneously, the presence of the variable-doped bipolar transport layer in the MPS diode of this invention also improves the reverse breakdown voltage. Attached Figure Description

[0015] The following is a brief explanation of the content and markings in each of the accompanying drawings in this specification:

[0016] Figure 1 This is a schematic diagram of the silicon carbide MPS diode with high surge current of the present invention.

[0017] Figure 2 A schematic diagram of the structure of a traditional silicon carbide MPS diode;

[0018] Figure 3 The forward current curve of the MPS diode;

[0019] Figure 4 Temperature curve of MPS diode under sinusoidal current waveform

[0020] Figure 5 The graph shows the relationship between reverse voltage and reverse current for an MPS diode.

[0021] The markings in the above figures are as follows: 1. Silicon carbide N+ substrate; 2. Silicon carbide N- epitaxial layer; 3. P+ implantation region; 4. Ohmic contact electrode; 5. Schottky contact electrode; 6. First bipolar transport layer; 7. Second bipolar transport layer; 8. Cathode ohmic contact electrode. Detailed Implementation

[0022] The following description, with reference to the accompanying drawings, details the specific implementation of the present invention, including the shape and structure of each component, the relative positions and connections between the parts, the function and working principle of each part, the manufacturing process, and the operation and use methods, to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the inventive concept and technical solution of the present invention.

[0023] like Figure 1 The diagram shows a schematic of the silicon carbide MPS diode layer structure with high surge current according to the present invention. It includes an ohmic contact electrode 4, a silicon carbide N+ substrate 1, a silicon carbide N- epitaxial layer 2, a Schottky contact electrode 5, multiple P+ injection regions 3, a first bipolar transport layer 6, a second bipolar transport layer 7, and a cathode ohmic contact electrode 5. The cathode ohmic contact electrode 5, the silicon carbide N+ substrate 1, and the silicon carbide N- epitaxial layer 2 are stacked sequentially from bottom to top. The multiple P+ injection regions 3 are spaced apart on the upper layer of the silicon carbide N- epitaxial layer 2. The ohmic contact electrode 4 is located above the multiple P+ injection regions 3, and the Schottky contact electrode 5 is located between the ohmic contact electrodes 4.

[0024] The core innovation of this invention lies in the provision of bipolar transport layers on both sides of the silicon carbide N-epitaxial layer 2. The first bipolar transport layer, located above the silicon carbide N-epitaxial layer 2 and containing the P+ implantation regions 3, is the first bipolar transport layer. The second bipolar transport layer 7 lies between the silicon carbide N-epitaxial layer 2 and the silicon carbide N+ substrate 1. The first bipolar transport layer 6 contains all the P+ implantation regions 3. The thickness of the bipolar transport layer is greater than the depth of the multiple P+ implantation regions 3, and its doping concentration is greater than that of the silicon carbide N-epitaxial layer 2. The impurity doping distribution is linear, with the doping concentration decreasing from top to bottom.

[0025] The aforementioned structure reduces the transition voltage (PN junction forward voltage) of the MPS diode from unipolar to bipolar operating state by incorporating a variable-doped bipolar transport layer with a higher doping concentration than the epitaxial layer 2 on the silicon carbide N-epitaxial layer 2. This allows the diode to enter the bipolar operating state at a lower forward current, reducing the diode's on-resistance, lowering its high-current operating temperature, and providing higher surge current resistance. Simultaneously, the bipolar transport layer also improves the diode's reverse breakdown voltage.

[0026] The present invention can also be improved as follows: preferably, the doping distribution of the first bipolar transport layer 6 and the second bipolar transport layer 7 is set to a linear distribution, with the doping concentration decreasing from top to bottom, and the highest doping concentration being the same as the doping concentration of the epitaxial layer. This improves the surge resistance of the diode while avoiding the reduction of Schottky current under normal operating conditions.

[0027] To facilitate the following Figure 2 The performance of the first conventional silicon carbide MPS diode shown is compared with that of the silicon carbide MPS diode of the present invention. In this embodiment, the SiC MPS diode is fabricated using the same doping level and the same size: the doping concentration of the silicon carbide N-epitaxial layer 2 is 2E16cm. -3The thickness of the silicon carbide N- epitaxial layer 2 is 6 micrometers; metallic Ti alloy is used as the Schottky contact electrode 5, and metallic Ni is used as the ohmic contact electrode 4; the thickness of the silicon carbide N+ substrate 1 is 180 micrometers, and the doping concentration is 1E20cm⁻¹. -3 The doping concentration in the P+ implantation region 3 is 5E19cm. -3 The width is 2.5 micrometers, the junction depth is 0.6 micrometers, and the spacing is 4 micrometers. The P+ implantation region 3 has a total of 2 P+ implantation rings; the doping concentration of the first bipolar transport layer 6 is 2E16cm. -3 Up to 1E16cm -3 The doping concentration of the second bipolar transport layer 7 is linearly distributed from high to low, with a thickness of 1 micrometer; the doping concentration of the second bipolar transport layer 7 ranges from 2E16cm⁻¹. -3 Up to 1E16cm -3 The distribution is linear from high to low, with a thickness of 1 micrometer.

[0028] Build using TCAD software Silvaco, such as Figure 1 , Figure 2 The device structure is such that a forward voltage is applied to the Schottky electrode of the diode, and the relationship curve between the forward voltage and the forward current is obtained, as shown in the figure. Figure 3 As shown. Curve A is the forward current curve of a conventional SiC MPS diode, and curve B is the forward current curve of the MPS diode in this embodiment of the patent. From Figure 3 It can be obtained, such as Figure 2 The conventional MPS diode shown has a forward conduction voltage of 1.34V and a PN junction conduction voltage of 5V at 15A, with a current of 110A. The MPS diode of the present invention has a forward conduction voltage of 1.39V and a PN junction conduction voltage of 4.5V at 15A, with a current of 90A.

[0029] It can be seen that the PN junction forward voltage of the silicon carbide MPS diode with high surge current in the embodiment of the present invention is reduced by about 10% compared with the first conventional MPS diode, while the forward voltage drop under a normal operating current of 15A is only increased by 3.7%, that is, the operating forward voltage drop is not increased much due to the bipolar transport layer.

[0030] The temperature curves of a conventional MPS diode and the MPS diode of this embodiment under a sinusoidal current waveform with a period of 10ms and a peak value of 115A show that, as Figure 4 As shown, curve A is the temperature curve of a conventional SiC MPS diode, and curve B is the temperature curve of the MPS diode of this patent embodiment. It can be seen that the peak temperature of the MPS diode in this embodiment is 870K, while the peak temperature of the conventional MPS diode reaches 1100K, a reduction of about 21%. It can be seen that the MPS diode of this patent embodiment has a lower chip temperature under high current and strong surge current resistance.

[0031] A voltage is applied to the ohmic contact of the diode cathode, and the relationship curve between reverse voltage and reverse current is obtained, as shown in the figure. Figure 5 As shown, curve B is the reverse current curve of a conventional SiC MPS diode, and curve A is the reverse current curve of the MPS diode of this patent embodiment. It can be seen that the reverse breakdown voltage of the MPS diode in this embodiment is 810V, while the reverse breakdown voltage of a conventional MPS diode is 780V, a reduction of approximately 4%. This demonstrates that the MPS diode of this patent embodiment has better reverse performance.

[0032] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A silicon carbide MPS diode with high surge current, comprising, in sequence, a cathode ohmic contact electrode, a silicon carbide N+ substrate, and a silicon carbide N- epitaxial layer, wherein a plurality of P+ injection regions are spaced apart on the silicon carbide N- epitaxial layer, and ohmic contact electrodes are disposed on the P+ injection regions, the gaps between the ohmic contact electrodes being filled by Schottky contact electrodes, characterized in that: Bipolar transport layers are provided on both sides of the silicon carbide N-epitaxial layer; The bipolar transport layer between the P+ implantation region and the silicon carbide N- epitaxial layer is the first bipolar transport layer, and the bipolar transport layer between the silicon carbide N- epitaxial layer and the silicon carbide N+ substrate is the second bipolar transport layer. The first bipolar transport layer includes the P+ implantation region, and the thickness of the bipolar transport layer is greater than the depth of the P+ implantation region. The doping concentration of the silicon carbide N-epitaxial layer is 2E16cm. -3 ; The impurity doping distribution of the first bipolar transport layer is linear, with the doping concentration decreasing from top to bottom. The doping concentration of the first bipolar transport layer decreases from 2E16cm⁻¹. -3 Up to 1E16cm -3 Linear distribution from high to low The impurity doping distribution of the second bipolar transport layer is linear, with the doping concentration decreasing from top to bottom. The doping concentration of the second bipolar transport layer decreases from 2E16cm⁻¹. -3 Up to 1E16cm -3 Linear distribution from high to low; The first bipolar transport layer and the second bipolar transport layer have the same thickness, which is 1 micrometer.

2. The silicon carbide MPS diode with high surge current according to claim 1, characterized in that: The doping concentration of the bipolar transport layers is lower than that of the silicon carbide N-epitaxial layers.

3. The silicon carbide MPS diode with high surge current according to claim 2, characterized in that: The first bipolar transport layer and the second bipolar transport layer have the same doping concentration.

4. The silicon carbide MPS diode with high surge current according to claim 3, characterized in that: The first bipolar transport layer and the second bipolar transport layer have the same impurity doping distribution.

5. The silicon carbide MPS diode with high surge current according to claim 1, 2, 3 or 4, characterized in that: The highest doping concentration of the bipolar transport layer is the same as that of the silicon carbide N-epitaxial layer.

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